The present invention relates generally to position indicating and guidance systems and in particular, to a control system and method providing positional and guidance information to a machine carrying a tool for movement along a predetermined path at a worksite using a single laser transmitter and a detector array.
Construction relies heavily on positioning data. Construction performance, in particular productivity and quality of work, is tied to the speed and accuracy of positioning methods being used. Standard surveying techniques are relatively slow, require highly skilled operators, and remain prone to human error.
In a prior art laser transmitter, a narrowly focused, horizontally rotating beam of laser energy is used to provide a reference plane. The rotating beam intercepts a vertically extending array of photodetectors in a laser receiver to mark the elevation of the receiver with respect to the laser beam. The array extends typically 4 to 8 inches. Accordingly, the available data is limited to elevation over a rather small vertical range, and thus due to plane tilting and alignment iteration, establishing grade with such a conventional laser system is time consuming.
In another prior art laser transmitter, planes of light are emitted, instead of just a line of light showing level. The planes of light provide enough angle information that an associated receiver can calculate plumb alignment, elevation, and slope to the transmitter. However, in both the former and latter systems, information regarding the relative distance and direction (azimuth) from the receiver to the transmitter is not established.
To establish distance and direction, machine operators typically follow pre-surveyed direction markings on the stakes, string lines, a laser beam from a pipe laser, or by triangulation using a second laser transmitter. Furthermore, in excavating operations, the conventional depth indicating system is a rotating laser plane with a single laser receiver to indicate if the vertically oriented boom and bucket are above, below or on the desired elevation, with or without grade. However, it is to be appreciated that the length of the photo-detection area of the single laser receiver limits the vertical operating range of such depth indicating systems to approximately ±2 and ±4 inches respectively. These narrow limits often result in the operator “searching for the beam” to regain depth indication.
Typically, direction of a machine, such as for example an excavator, is provided by pre-surveyed markings on stakes, string lines, or an additional laser transmitter, such as a pipe laser. However, these methods have known drawbacks. Line destruction resulting from construction site activity may result in digging delays, and using an additional laser is expensive. Furthermore, grade using a laser is established by sloping the laser energy plane until the sloped plane is pointed in the desired direction. This setup operation may require several checks, with an additional hand-held detector, and rotational iterations to achieve the desired grade. Accordingly, establishing distance, direction, and grade using a conventional laser system, stakes, string lines, pipe lasers, or a second transmitter is time consuming and adds additional costs.